1. Field of the Invention
This invention relates to a polypropylene-base resin composition, and more specifically to a polypropylene-base resin composition suitable for use in the production of molded articles having excellent paintability. This invention also relates to a molded polypropylene-base resin article, especially, a car bumper, which has excellent paintability.
2. Description of the Prior Art
Polypropylene-base resins are excellent in weight reduction, durability, safety, moldability, economy and the like and their molded articles are hence widely used as various industrial elements, parts, components and so on typified by car parts and components such as bumpers. Many of such molded articles are colored in black or similar dark colors in view of their color tones, weatherability, etc. Reflecting recent needs on the market, there is an ever-increasing demand for painting such molded articles to impart high-quality appearance thereto from the aesthetic consideration. Accordingly, it is now indispensable to impart paintability to them.
These days, molded polypropylene-base resin articles are in many instances painted by treating their surfaces with a halogen-containing organic solvent such as trichloroethylene or trichloroethane, followed by their primer coating and topcoating [Mod. Plas., 39 (No. 9) 153 (1962)]. With a view toward solving the problem of environmental pollution due to such halogen-containing organic solvents and reducing the manufacturing cost by simplifying their painting process, it has been started using a new process in which subsequent to plasma surface treatments of molded article, their topcoating are carried out [J. Appl. Poly. Sci., 11 1461 (1967) and U.S. Pat. No. 4,465,715].
Most polypropylene-base resins have already been colored with inorganic or organic colorants or mixtures thereof prior to their painting, no matter whether they are painted at their entire surfaces or at their limited surface areas. It is a common practice to incorporate carbon black or a black or blackish pigment consisting primarily of carbon black, particularly, in elements, parts, components and the like which are used outdoors, in view of the manner of their use and with a view to making improvements to their weatherability. Under the circumstances, carbon black is incorporated in large proportions in polypropylene-base resins.
It has however been found that the paintability of a molded article of a polypropylene-base resin added with a large amount of carbon black is considerably reduced when a paint is applied thereto subsequent to its plasma treatment.